feat: add comprehensive tutorial page with step-by-step guides

New tutorial.html covering:
- Three installation paths (USB, one-click script, manual)
- Complete manual installation from scratch (Node.js, npm mirrors, OpenClaw)
- Per-provider model setup guides (DeepSeek, Kimi, Qwen, OpenRouter)
- Per-platform chat bot tutorials (QQ, Telegram, Feishu, WeChat, Discord)
- Daily usage scenarios, skills system, cron jobs
- Troubleshooting guide, security hardening, VPS deployment
- Command quick reference and config file reference

Designed to complement hello-claw (datawhalechina) by filling gaps:
beginner-friendly manual install, detailed per-platform setup, and
portable USB-specific guidance.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

website/index.html

@@ -659,6 +659,7 @@
     </p>
     <p style="margin-top: 8px;">
         <a href="https://github.com/dongsheng123132/u-claw">GitHub</a> ·
+        <a href="tutorial.html">教程</a> ·
         <a href="guide.html">使用指南</a> ·
         <a href="https://github.com/openclaw/openclaw">OpenClaw</a> ·
         <a href="mailto:hefangsheng@gmail.com">hefangsheng@gmail.com</a>